Infinitely variable control switch



June 30, 1959 W. P. SOMERS ET AL INFINITELY VARIABLE CONTROL SWITCH Filed Aug. 26, 1957 INVENTORS WILLIAM R SOMERS 8 WILLARD a. HOLT THEIR ATTORNEY United 2,892,918 INFINITELY VARIABLE CONTROL swrrcu Application August 26, 1957, Serial No. 680,082

8 Claims. (Cl. 219-20) This invention relates to heating unit control switches, and more particularly to a device for periodically supplying current to an electric heating unit for selectively variable intervals of time.

Infinitely variable heat control switches of the type including a pair of reciprocating contacts arranged to periodically complete the circuit to an electric heating unit are, of course, well known in the art. In some switches of this type the contacts are reciprocated by a motor driven cam while in others a periodically heated bimetal blade is utilized for this purpose. While the latter power element is generally less expensive than the former, conventional bimetal powered infinite heat switches are inherently sensitive to changes in line volt age and ambient temperature, and hence present a problem insofar as exact heat output settings are concerned. Furthermore, such switches have certain disadvantages stemming from the difficulty of obtaining fast cycling action when the bimetal must operate relatively heavy line voltage contacts, and the related difficulty of providing a full range of heat outputs with a bimetal having a heat up and cool down cycle requiring a relatively long minimum time interval.

Accordingly, a principal object of this invention is to provide a bimetal powered control device for electric heating units so arranged that its performance is substantially unaffected by variations in line voltage or ambient temperature.

Another object of this invention is to provide a bimetal powered control device for electric heating units so arranged that a full range of heat outputs as well as positive contact actuation may be obtained.

Further objects and advantages of this invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims appended to and forming a part of this specification.

Briefly stated, in accordance with one aspect of this invention there is provided a pair of spaced contacts, manually operable means for varying the spacing therebetween, and a bimetal powered movable contact located between the pair of contacts so that it engages first one and then the other of spaced contacts during its travel between two extremes of movement. Inasmuch as the heating unit controlled thereby is connected so as to be energized each time the bimetal powered contact engages one of the associated pair of contacts, the proportion of total on time to total ofi timeis unaffected by changes in line voltage or ambient temperature, and the cycling time is in efiect cut inhalf.

For a better understanding of this invention reference may be made to the following descriptionand the accon1- panying drawing in which:

Fig. 1 is a fragmentary elevational view, partly in section, showing an electric range in which is mounted a control switch constructed in accordance with this invention;

Patent Fig. 2. is a front elevation view of the control switch shown in Fig. 1;

Fig. 3- is an exploded view, in perspective, of theswitch shown in Figs. 1 and 2;

Fig. 4 isa fragmentary sectional view taken along the lines 44 in Fig. 2;

Fig. 5 is a side elevation view of the switch shown in Fig. 2; and

Fig. 6 is a diagrammatic view of an electric heating circuit in which the switch of this invention may be utlized.

Referring to the drawing, the reference numeral 1 designates an electric range provided with a surface heating unit 2 and a heating unit control switch 3 constructed-in accordance with the present invention.

Control switch 3 comprises a suitable base structure, preferably formed of insulating material, including a lower support portion 4, an upright support portion 5 and lateral-ling projecting support portions 6, 7 and 8. Mounted on support portion 7 are a pair of generally parallel cantilever arms designated by the numerals 9 and 10, upon which are mounted spaced electrical contacts 11 and 12 respectively. Contacts 11 and 12 cooperate with and are engageable by a movable contact 13 mounted on cantilever arm 14 which is positioned between arms 9 and 10 in generally parallel relation thereto. Arm 14 is formed of a suitable bimetallic material, such as a laminated strip of iron and copper, and is secured to support portion 6 so that its free end is movable between a first position in which contact 13 engages contact 11 and a second position in which contact 13 engages contact 12. Arranged in heat transfer relation with bimetal arm 14 is a heating element 15 so that the free end of arm 14 may be periodically reciprocated by periodic energization of heating element 15. In some instances it may be desirable to increase the cooling rate of arm 14 so that after each heating cycle it rapidly returns to its cold position, and this may be accomplished by the provision of a heat radiating element 16, which may be a copper wire screen or other means having a plurality of heat radiating surfaces.

From the arrangement described thus far, it will be seen that movable contact 13 is arranged to be reciprocated by bimetallic means between a first position in engagement with contact 11 and in a second position in engagement with contact 12, and that by energizing heating element 15 for a period of time sufiicient to effect this movement periodic energization of a circuit including these contacts may be accomplished. Energization of heating element 15 is preferably controlled by means of switch contacts 17 and 1d mounted on movable arm 19 and support portion 8. Contacts 17 and 18 are normally closed but are arranged to be opened each time contact 13 is moved a predetermined distance between contacts 11 and 12. Thus, the free end of arm 19 includes a bifurcated portion 20 arranged to cooperate with a finger 20a secured to bimetal arm 14 so as to provide a lost motion connection between these two arms. Arm 19 is biased so as to hold contacts 17 and 18 in engagement until movement of bimetal arm 14' toward contact 11 causes finger 20a to engage bifurcated portion 20' of arm 19, and thus disengage the contacts. Snap action of these contacts is desirable and may be achieved by the provision of a magnet 21 mounted on support portion 8 so as to cooperate with a keeper 2?. carried by arm 19. Thus it will be seen that current for heating element 15 will be supplied through contacts 17 and 13' during initial movement of bimetal arm 14 toward contact 11', and that this current will be interrupted as contact 13 approaches contact 11' so that bimetalarm 14 will return to itsinitial position during the interval when heating element 15 is de-energized.

As shown in Fig. 6 of the drawing, contacts 11 and 12 ice are connected together and are adapted to be connected in a heating circuit so as to control surface heating unit 2, for example. Thus, contact 13 may be connected to heating unit 2 while contacts 11 and 12 may be connected to a power supply line L1, so that each time contact 13 engages either contact 11 or contact 12 power is supplied to heating unit 2. Bimetallic heater element 15 and control contacts 17 and 18 are also connected across power supply lines L1, L2 so that each time these contacts close heat is supplied to heater 15.

In order to provide a range of heat outputs from off to full power, suitable manually operable means for varying the spacing between contacts 11 and 12 are provided, such as a cam 23 positioned between arms 9 and 10. Cam 23 may be manually rotated by means of a handle 24 arranged to project through a slot in the range body, or any other suitable means. Handle 24 includes a portion 24 extending through support portion 5, a U-shaped connecting portion 26, and a leg portion to which is secured a movable stop element 27. Stop element 27 cooperates with arm 19, and engages this arm only when control member 24 is moved to its off position so as to positively disengage contacts 17 and 18. In the off position shown in Fig. 1 of the drawing contacts 11 and 12 are spaced so far apart by cam 23 that contact 13 cannot engage either of them and hence both surface heat" ing unit 2 and bimetal heater 15 are positively disconnected from the power supply L1, L2. Upward movement of handle 24 (as viewed in Fig. 1) permits arms 9 and to move toward each other inasmuch as they are biased against cam 23, and thus contacts 11 and 12 may be positioned at various distances from each other, including a full power position in which they are so close that contact 13 maintains contact with either contact 11 or contact 12 substantially 100% of the time. In order to provide for snap action of these contacts, a magnet 28 carried on finger 20b may be provided, this magnet being arranged to cooperate with keeper 29 secured to the free end of arm 9 and with keeper 30 secured to the free end of arm 10.

From the foregoing description it will be evident that control switch 3 provides an infinite number of heat output levels in the range between its ofi? position and its full power position, and that at each power level current is supplied to heating unit 2 twice during each complete cycle of movement of the bimetallic arm 14. Inasmuch as contact 13 moves from contact 12 to contact 11 each time bimetal 14 is heated by heater 15, and returns to engagement with contact 12 as bimetal 14 cools, it will be seen that a change in voltage or ambient temperature will result in an increase in the time intervals during which contacts 12 and 13 are engaged and a decrease in the intervals contacts 11 and 13 are engaged, or vice versa. Therefore, it will be evident that changes in line voltage or ambient temperature will produce some change in cycle time but will not appreciably affect the otF to on ratio.

While we have shown and described a particular embodiment of our invention, we do not desire the invention to be limited to the particular construction disclosed, and we intend by the appended claims to cover all modifications within the true spirit and scope of the invention.

What we claim is:

1. In a device for periodically supplying current from a two line source of electric power to an electric heating unit or the like for selectively variable intervals of time, the combination comprising first and second spaced apart contacts movable relative to each other and adapted to be connected to one line of said source of electric power, manually operable means for varying the spacing between said first and second contacts, a movable contact adapted to be connected to said electric heating unit which is connected to the other line of said source of electric power,

4 said movable contact being supported between and engageable with said first and second contacts, and bimetallic means for periodically reciprocating said movable contact between one position in which it engages said first contact and another position in which it engages said second contact.

2. A device as defined in claim 1 in which said bimetallic means includes a bimetal element, a heating element in heat transfer relation therewith, and switch means adapted to connect said heating element to a source of electric power, said switch means being operable to energize said heating element when said movable contact is in engagement with said first contact, and to de-energize said heating element as said movable contact approaches said second contact.

3. A device as defined in claim 2 in which said bimetal element is provided with heat radiator means in heat transfer relation therewith.

4. In a device for periodically supplying current from a two line source of electric power to an electric heating unit or the like for selectively variable intervals of time, the combination comprising first and second generally parallel cantilever arms, a bimetal cantilever arm positioned between said first and second arms in generally parallel relation thereto, manually operable means for varying the spacing between said first and second arms, a heating element arranged in heat transfer relation with said bimetal arm, first and second electrical contacts se cured to the free ends of said first and second arms respectively and adapted to be connected to one line of said source of electric power, a third electrical contact secured to the free end of said bimetal arm and adapted to be connected to said electric heating unit which is connected to the other line of said source of electric power, said first and second contacts being positioned so as to, be engageable with said third contact, and means for periodically energizing said heating element whereby said bimetal arm periodically reciprocates between one position in which said first and third contacts are in engagement to another position in which said second and third contacts are in engagement.

5. A device as defined in claim 4 in which said means for periodically energizing said heating element includes a pair of switch contacts adapted to connect said heating element to a source of electric power, one of said switch contacts being movable by said bimetal arm out of engagement with the other of said switch contacts after said bimetal arm has moved a predetermined distance away from said first arm.

6. A device as defined in claim 4 in which said manually operable means includes a rotatable cam having a pair of cam faces engageable with said first and second arms.

7. A device as defined in claim 4 in which said bimetal arm is provided with heat radiator means in heat transfer relation therewith.

8. A device as defined in claim 5 in which said mann ally operable means includes a rotatable cam having a pair of cam faces engageable with said first and second arms, and a stop element adapted to hold said pair of switch contacts in disengaged relation when said manually operable means is positioned so as to provide maximum spacing between said first and second arms.

References Cited in the file of this patent UNITED STATES PATENTS 2,281,319 Newell Apr. 28, 1942 2,606,990 Akeley Aug. 12, 1952 2,762,885 Foster Sept. 11, 1956 2,793,271 Muller et a1 May 21, 1957 2,806,119 Williams Sept. 10, 1957 2,813,172 Wojcik Nov. 12, 1957 

